Method and apparatus for reproducing/recording a text subtitle stream

ABSTRACT

In one embodiment, a method of reproducing text subtitle streams. The method includes receiving at least one text subtitle stream from an external source. Each text subtitle stream including a style segment defining a group of region styles and a plurality of presentation segments. Each presentation segment having at least one region of text and each region of text being linked to a selected one of the group of region styles. The style segment further defining palette information. Each presentation segment having a palette update flag which indicates whether to use the palette information defined in the style segment or to use new palette information when reproducing the each presentation segment. Thereafter, the method calls for decoding the text subtitle stream using the style segment defining the group of region styles and the presentation segment including the palette update flag.

FOREIGN PRIORITY INFORMATION

This application claims the benefit of the Korean Patent Application No.10-2004-0020890, filed on Mar. 26, 2004, which is hereby incorporated byreference as if fully set forth herein.

DOMESTIC PRIORITY INFORMATION

This is a continuation application of application Ser. No. 11/070,242filed Mar. 3, 2005, the entire contents of which are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording medium, and moreparticularly, to a recording medium and method and apparatus forreproducing a text subtitle stream recorded on the recording medium.Although the present invention is suitable for a wide scope ofapplications, it is particularly suitable for recording the textsubtitle stream file within the recording medium and effectivelyreproducing the recorded text subtitle stream.

2. Discussion of the Related Art

Optical discs are widely used as an optical recording medium forrecording mass data. Presently, among a wide range of optical discs, anew high-density optical recording medium (hereinafter referred to as“HD-DVD”), such as a Blu-ray Disc (hereafter referred to as “BD”), isunder development for writing and storing high definition video andaudio data. Currently, global standard technical specifications of theBlu-ray Disc (BD), which is known to be the next generation technology,are under establishment as a next generation optical recording solutionthat is able to have a data significantly surpassing the conventionalDVD, along with many other digital apparatuses.

Accordingly, optical reproducing apparatuses having the Blu-ray Disc(BD) standards applied thereto are also being developed. However, sincethe Blu-ray Disc (BD) standards are yet to be completed, there have beenmany difficulties in developing a complete optical reproducingapparatus. Particularly, in order to effectively reproduce the data fromthe Blu-ray Disc (BD), not only should the main AV data as well asvarious data required for a user's convenience, such as subtitleinformation as the supplementary data related to the main AV data, beprovided, but also managing information for reproducing the main dataand the subtitle data recorded in the optical disc should be systemizedand provided.

However, in the present Blu-ray Disc (BD) standards, since preferredmethods of creating the supplementary data, particularly the subtitlestream file, are yet to be completed, there are many restrictions in thefull-scale development of a Blu-ray Disc (BD) basis optical reproducingapparatus. And, such restrictions cause problems in providing thesupplementary data such as subtitles to the user.

SUMMARY OF THE INVENTION

The present invention relates to a method of reproducing text subtitlestreams.

In one embodiment, the method includes receiving at least one textsubtitle stream from an external source. Each text subtitle streamincluding a style segment defining a group of region styles and aplurality of presentation segments. Each presentation segment has atleast one region of text with each linked to a selected one of the groupof region styles. The style segment has palette information such thateach presentation segment has a palette update flag which indicateswhether to use the palette information defined in the style segment orto use new palette information when reproducing the each presentationsegment. Thereafter, the method includes decoding the text subtitlestream using the style segment defining the group of region styles andthe presentation segment including the palette update flag.

In one embodiment, the invention relates to a method of recording textsubtitle streams. The method includes receiving at least one textsubtitle stream from an external source. Each text subtitle stream has astyle segment defining a group of region styles and a plurality ofpresentation segments. Each presentation segment contains at least oneregion of text and each region of text being linked to a selected one ofthe group of region styles. The style segment further defines paletteinformation, and each presentation segment further contains a paletteupdate flag which indicates whether to use the palette informationdefined in the style segment or to use new palette information whenreproducing the each presentation segment. Thereafter, the methodincludes recording the received text subtitle stream in a recordingmedium.

In one embodiment, the present invention relates to an apparatus forreproducing a text subtitle stream. The apparatus has a decoderconfigured to decode the text subtitle stream from the external source.The text subtitle stream including a style segment defining a group ofregion styles and a plurality of presentation segments. Eachpresentation segment containing at least one region of text and eachregion of text being linked to a selected one of the group of regionstyles. The style segment further defines palette information, and eachpresentation segment further contains a palette update flag whichindicates whether to use the palette information defined in the stylesegment or to use new palette information when reproducing the eachpresentation segment. A controller is configured to control operation ofthe decoder to receive the text subtitle stream from a receiver anddecode the text subtitle stream using the region styles defined in thestyle segment and the palette update flag defined in the presentationsegment.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates a structure of the data files recorded in an opticaldisc according to the present invention;

FIG. 2 illustrates data storage areas of the optical disc according tothe present invention;

FIG. 3 illustrates a text subtitle and a main image presented on adisplay screen according to the present invention;

FIG. 4 illustrates a schematic diagram illustrating reproduction controlof a text subtitle stream according to the present invention;

FIGS. 5A to 5C illustrate applications of the reproduction controlinformation for reproducing the text subtitle stream according to thepresent invention;

FIG. 6 illustrates the structure of a text subtitle stream fileaccording to the present invention;

FIGS. 7A and 7B illustrate applications of a set of palette informationto the structure of the text subtitle stream file according to thepresent invention;

FIG. 8 illustrates a syntax of the text subtitle stream file accordingto the present invention;

FIGS. 9A to 9D illustrate another example of syntax of the text subtitlestream file according to the present invention;

FIG. 10A illustrates another example of syntax of the text subtitlestream file according to the present invention;

FIG. 10B illustrates an example of a syntax of a region subtitle amongthe text subtitle stream file according to a first embodiment of thepresent invention; and

FIGS. 11A and 11B illustrate an optical recording and/or reproducingapparatus including a reproduction of the text subtitle stream fileaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts. In addition,although the terms used in the present invention are selected fromgenerally known and used terms, some of the terms mentioned in thedescription of the present invention have been selected by the applicantat his or her discretion, the detailed meanings of which are describedin relevant parts of the description herein. Furthermore, it is requiredthat the present invention is understood, not simply by the actual termsused but by the meaning of each term lying within.

In this detailed description, “recording medium” refers to all types ofmedium that can record data and broadly includes all types of mediumregardless of the recording method, such as an optical disc, a magnetictape, and so on. Hereinafter, for simplicity of the description of thepresent invention, the optical disc and, more specifically, the “Blu-raydisc (BD)” will be given as an example of the recording medium proposedherein. However, it will be apparent that the spirit or scope of thepresent invention may be equally applied to other types of recordingmedium.

In this detailed description, “main data” represent audio/video (AV)data that belong to a title (e.g., a movie title) recorded in an opticaldisc by an author. In general, the AV data are recorded in MPEG2 formatand are often called AV streams or main AV streams. In addition,“supplementary data” represent all other data required for reproducingthe main data, examples of which are text subtitle streams, interactivegraphic streams, presentation graphic streams, and supplementary audiostreams (e.g., for a browsable slideshow). These supplementary datastreams may be recorded in MPEG2 format or in any other data format.They could be multiplexed with the AV streams or could exist asindependent data files within the optical disc.

A “subtitle” represents caption information corresponding to video(image) data being reproduced, and it may be represented in apredetermined language. For example, when a user selects an option forviewing one of a plurality of subtitles represented in various languageswhile viewing images on a display screen, the caption informationcorresponding to the selected subtitle is displayed on a predeterminedportion of the display screen. If the displayed caption information istext data (e.g., characters), the selected subtitle is often called a“text subtitle”. Also, in the present invention, “palette information”refers to color information and opacity information, which are providedto the user, when the text subtitle data is reproduced onto the screen.According to the present invention, a plurality of text subtitle streamsin MPEG2 format may be recorded in an optical disc, and they may existas a plurality of independent stream files. Each “text subtitle streamfile” is created and recorded within an optical disc. And, the purposeof the present invention is to provide a method and apparatus forreproducing the recorded text subtitle stream file.

FIG. 1 illustrates a file structure of the data files recorded in aBlu-ray disc (hereinafter referred to as “BD”) according to the presentinvention. Referring to FIG. 1, at least one BD directory (BDMV) isincluded in a root directory (root). Each BD directory includes an indexfile (index.bdmv) and an object file (MovieObject.bdmv), which are usedfor interacting with one or more users. For example, the index file maycontain data representing an index table having a plurality ofselectable menus and movie titles. Each BD directory further includesfour file directories that include audio/video (AV) data to bereproduced and various data required for reproduction of the AV data.

The file directories included in each BD directory are a streamdirectory (STREAM), a clip information directory (CLIPINF), a playlistdirectory (PLAYLIST), and an auxiliary data directory (AUX DATA). Firstof all, the stream directory (STREAM) includes audio/video (AV) streamfiles having a particular data format. For example, the AV stream filesmay be in the form of MPEG2 transport packets and be named as “*.m2ts”,as shown in FIG. 1. The stream directory may further include one or moretext subtitle stream files, where each text subtitle stream fileincludes text (e.g., characters) data for a text subtitle represented ina particular language and reproduction control information of the textdata. The text subtitle stream files exist as independent stream fileswithin the stream directory and may be named as “*.m2ts” or “*.txtst”,as shown in FIG. 1. An AV stream file or text subtitle stream fileincluded in the stream directory is often called a clip stream file.

Next, the clip information directory (CLIPINF) includes clip informationfiles that correspond to the stream files (AV or text subtitle) includedin the stream directory, respectively. Each clip information filecontains property and reproduction timing information of a correspondingstream file. For example, a clip information file may include mappinginformation, in which presentation time stamps (PTS) and source packetnumbers (SPN) are in a one-to-one correspondence and are mapped by anentry point map (EPM), depending upon the clip type. Using the mappinginformation, a particular location of a stream file may be determinedfrom a set of timing information (In-Time and Out-Time) provided by aPlayItem or SubPlayItem, which will be discussed later in more details.In the industry standard, each pair of a stream file and itscorresponding clip information file is designated as a clip. Forexample, 01000.clpi included in CLIPINF includes property andreproduction timing information of 01000.m2ts included in STREAM, and01000.clpi and 01000.m2ts form a clip.

Referring back to FIG.1, the playlist directory (PLAYLIST) includes oneor more PlayList files (*.mpls), where each PlayList file includes atleast one PlayItem that designates at least one main AV clip and thereproduction time of the main AV clip. More specifically, a PlayItemcontains information designating In-Time and Out-Time, which representreproduction begin and end times for a main AV clip designated byClip_Information_File_Name within the PlayItem. Therefore, a PlayListfile represents the basic reproduction control information for one ormore main AV clips. In addition, the PlayList file may further include aSubPlayItem, which represents the basic reproduction control informationfor a text subtitle stream file. When a SubPlayItem is included in aPlayList file to reproduce one or more text subtitle stream files, theSubPlayItem is synchronized with the PlayItem(s). On the other hand,when the SubPlayItem is used to reproduce a browsable slideshow, it maynot be synchronized with the PlayItem(s). According to the presentinvention, the main function of a SubPlayItem is to control reproductionof one or more text subtitle stream files.

Lastly, the auxiliary data directory (AUX DATA) may includesupplementary data stream files, examples of which are font files (e.g.,aaaaa.font or aaaaa.otf), pop-up menu files (not shown), and sound files(e.g., Sound.bdmv) for generating click sound. The text subtitle streamfiles mentioned earlier may be included in the auxiliary data directoryinstead of the stream directory.

FIG. 2 illustrates data storage areas of an optical disc according tothe present invention. Referring to FIG. 2, the optical disc includes afile system information area occupying the inmost portion of the discvolume, a stream area occupying the outmost portion of the disc volume,and a database area occupied between the file system information areaand the stream area. In the file system information area, systeminformation for managing the entire data files shown in FIG. 1 isstored. Next, main data and supplementary data (i.e., AV streams and oneor more text subtitle streams) are stored in the stream area. The maindata may include audio data, video data, and graphic data. And, thesupplementary data (i.e., the text subtitle) is independently stored inthe stream area without being multiplexed with the main data. Thegeneral files, PlayList files, and clip information files shown in FIG.1 are stored in the database area of the disc volume. As discussedabove, the general files include an index file and an object file, andthe PlayList files and clip information files include informationrequired to reproduce the AV streams and the text subtitle streamsstored in the stream area. Using the information stored in the databasearea and/or stream area, a user is able to select a specific playbackmode and to reproduce the main AV and text subtitle streams in theselected playback mode.

Hereinafter, the structure of the text subtitle stream file according tothe present invention will be described in detail. First of all, thecontrol information for reproducing the text subtitle stream will benewly defined. Then, the detailed description of the method of creatingthe text stream file including the newly defined control information,and the method and apparatus of reproducing the text subtitle stream forreproducing the recorded stream file will follow. FIG. 3 illustrates atext subtitle and a main image presented on a display screen accordingto the present invention. The main image and the text subtitle aresimultaneously displayed on the display screen when a main AV stream anda corresponding text subtitle stream are reproduced in synchronization.

FIG. 4 is a schematic diagram illustrating reproduction control of amain AV clip and text subtitle clips according to the present invention.Referring to FIG. 4, a PlayList file includes at least one PlayItemcontrolling reproduction of at least one main AV clip and a SubPlayItemcontrolling reproduction of a plurality of text subtitle clips. One oftext subtitle clip 1 and text subtitle clip 2, shown in FIG. 4, forEnglish and Korean text subtitles may be synchronized with the main AVclip such that a main image and a corresponding text subtitle aredisplayed on a display screen simultaneously at a particularpresentation time. In order to display the text subtitle on the displayscreen, display control information (e.g., position and sizeinformation) and presentation time information, examples of which areillustrated in FIG. 5A to FIG. 5C, are required.

FIG. 5A illustrates a dialog presented on a display screen according tothe present invention. A dialog represents entire text subtitle datadisplayed on a display screen during a given presentation time. Ingeneral, presentation times of the dialog may be represented inpresentation time stamps (PTS). For example, presentation of the dialogshown in FIG. 5A starts at PTS (k) and ends at PTS (k+1). Therefore, thedialog shown in FIG. 5A represents an entire unit of text subtitle datawhich are displayed on the display screen between PTS (k) and PTS (k+1).A dialog includes a maximum of 100 character codes in one text subtitle.

In addition, FIG. 5B illustrates regions of a dialog according to thepresent invention. A region represents a divided portion of textsubtitle data (dialog) displayed on a display screen during a givenpresentation time. In other words, a dialog includes at least oneregion, and each region may include at least one line of subtitle text.The entire text subtitle data representing a region may be displayed onthe display screen according to a region style (global style) assignedto the region. The maximum number of regions included in a dialog shouldbe determined based on a desired decoding rate of the subtitle databecause the greater number of regions generally results in a lowerdecoding ratio. For example, the maximum number of regions for a dialogmay be limited to two in order to achieve a reasonably high decodingrate. Accordingly, the maximum number of regions within a single dialogis limited to 2 because of the decoding load, when the text subtitlestream is reproduced. In another embodiment of the present invention, amaximum of n number (wherein, n>2) of regions may exist within a singledialog.

FIG. 5C illustrates style information for regions of a dialog accordingto the present invention. Style information represents informationdefining properties required for displaying at least a portion of aregion included in a dialog. Some of the examples of the styleinformation are position, region size, background color, text alignment,text flow information, and many others. The style information may beclassified into region style information (global style information) andinline style information (local style information).

Region style information defines a region style (global style) which isapplied to an entire region of a dialog. For example, the region styleinformation may contain at least one of a region position, region size,font color, background color, text flow, text alignment, line space,font name, font style, and font size of the region. For example, twodifferent region styles are applied to region 1 and region 2, as shownin FIG. 5C. A region style with position 1, size 1, and color=blue isapplied to Region 1, and a different region style with position 2, size2, and color=red is applied to Region 2.

On the other hand, local style information defines an inline style(local style) which is applied to a particular portion of text stringsincluded in a region. For example, the inline style information maycontain at least one of a font type, font size, font style, and fontcolor. The particular portion of text strings may be an entire text linewithin a region or a particular portion of the text line. Referring toFIG. 5C, a particular inline style is applied to the text portion“mountain” included in Region 1. In other words, at least one of thefont type, font size, font style, and font color of the particularportion of text strings is different from the remaining portion of thetext strings within Region 1.

Accordingly, the above-described text data is recorded and described asa “text string” depending upon whether a specific inline style exists.FIG. 6 illustrates a text subtitle stream file (e.g., 10001.m2ts shownin FIG. 1) according to the present invention. The text subtitle streamfile may be formed of an MPEG2 transport stream including a plurality oftransport packets (TP), all of which have a same packet identifier(e.g., PID=0x18xx). When a disc player receives many input streamsincluding a particular text subtitle stream, it finds all the transportpackets that belong to the text subtitle stream using their PIDs.Referring to FIG. 6, each sub-set of transport packets form a packetelementary stream (PES) packet. One of the PES packets shown in FIG. 6corresponds to a dialog style segment (DSS) defining a group of regionstyles. All the remaining PES packets after the second PES packetcorrespond to dialog presentation segments (DPSs)

In the above-described text subtitle stream structure of FIG. 6, each ofthe dialog information shown in FIGS. 5A to 5C represent a dialogpresentation segment (DPS). And, the style information included in thedialog information represents a set of information that links any one ofthe plurality of region style sets defined in the dialog style segment(DSS), which can also be referred to as “region_style_id”, and inlinestyles. Accordingly, in the present invention, a region style set andpalette information, which are applied to the dialog presentationsegment (DPS), are recorded in the dialog style segment (DSS), whichwill now be described in detail.

FIG. 7A illustrates structures of the dialog style segment (DSS)recorded in the text subtitle stream, and of the dialog presentationsegment (DPS). Accordingly, a detailed syntax of the text subtitlestream will be described in a later process with reference to FIG. 8.More specifically, the dialog style segment (DSS) includes a maximum of60 sets of region style is recorded therein, each of which is describedby a region_style_id. A region style set, which includes diverse regionstyle information, and a user changeable style set are recorded in eachregion_style_id. Herein, detailed contents of the region styleinformation will be described in FIG. 9B, and detailed contents of theuser changeable style information will be described in FIG. 9C.

In addition, the dialog style segment includes palette information whichis commonly applied within the corresponding text subtitle stream, andthe palette information includes color information (Y, Cr and Cb values)and transparency information (T value) for each palette entry ID(palette_entry_ID). And, in order to indicate (or display) a specificcolor information among the style information, the correspondingpalette_entry_ID is designated, thereby enabling the desired color to berepresented. Furthermore, the dialog presentation segment (DPS) includestext data and timing information indicating the presentation time of thetext data (i.e., PTS set). The dialog presentation segment (DPS) alsoincludes information linking any one of the style information for eachregion and the specific region style information included in theabove-described dialog style.

And, generally, the dialog presentation segment (DPS) is commonlyapplied with the palette information defined in the above-describeddialog style segment (DSS). However, a separate palette informationshould also be newly defined and applied to the dialog presentationsegment (DPS). Herein, information indicating such modification (orupdate) of the palette information is referred to as a“palette_update_flag”. More specifically, when palette_update_flag=0b,the common palette information defined at the dialog style segment (DSS)is applied as it is without any modification (or update). Conversely,when palette_update_flag=1b, a new palette information (i.e., palette()) that is applied to the corresponding dialog style segment (DSS) isdefined and used.

At this point, the newly defined palette information is recorded byupdating only the palette information required by the correspondingdialog presentation segment (DPS). And, when the corresponding dialogpresentation time is ended, the common palette information provided fromthe DSS is applied to the subsequent DPS. More specifically, whenpalette_update_flag=0b, the common palette information provided from theDSS is applied. And, when palette_update_flag=1b, a palette informationnewly defined in the corresponding dialog presentation segment (DPS) isapplied.

Therefore, referring to FIG. 7A, in DPS #1, DPS #2, and DPS #6, theregion style applied to each set of text data (Text data #1, Text data#2, and Text data #3) is respectively linked and applied to each ofregion_style_id=k, region_style_id=n, and region_style_id=m within thedialog presentation segment (DPS). And, since palette_update_flag=0b,the common palette information provided from the DSS is used. On theother hand, in DPS #3, DPS #4, and DPS #5, the region style applied toeach text data (Text data #2) is respectively linked and applied toregion_style_id=n within the dialog presentation segment (DPS). And,since palette_update_flag=1b, the palette information newly defined inthe corresponding DPS is applied, instead of the common paletteinformation provided from the DSS. Meanwhile, the style informationlinked by the region style ID (region_style_id) is equally applied toall of the text data within the corresponding region (i.e., the globalstyle information). However, when the style information for a specifictext string within the text data is requested to be changed (ormodified), an inline style information, which is a local styleinformation that is applied only to the text string, is defined andused.

FIG. 7B illustrates a usage of the palette information of DPS #1 to DPS#6 as shown in FIG. 7A and, most particularly, illustrates a method forrepresenting a fading effect showing Fade In and Fade Out effects. Morespecifically, referring to FIG. 7B, in DPS #1 and DPS #2,palette_update_flag=0b is applied, thereby using the common paletteinformation provided from the DSS. However, when DPS #2 is processedwith a fade out effect, palette_update_flag=1b is applied to each of DPS#3, DPS #4, and DPS #5, so as to gradually modify (or change) thepalette information, which designates color and/or transparency, therebyproducing (or producing) the fade out effect. Therefore, the process ofnewly defining and modifying (or changing) only the palette information,as shown in DPS #3, DPS #4, and DPS #5, and redefining theabove-described style information and text data without anymodifications, as those used in DPS #2, is also referred to as a“palette only Display update”.

Accordingly, when palette_update_flag=1b, such as in DPS #1, DPS #2, andDPS #6, the DPS using the common palette information defined in the DSSmay be named as a first dialog presentation segment (DPS). And, whenpalette_update_flag=0b, such as in DPS #3, DPS #4, and DPS #5, the DPShaving a specific palette information within the corresponding DPS andusing the specific palette information may be named as a second dialogpresentation segment (DPS). Therefore, it is apparent that the textsubtitle stream is formed of the dialog style segment (DSS), the firstdialog presentation segment (DPS), and the second dialog presentationsegment (DPS). Furthermore, considering the display time of each DPS,when palette_update_flag=0b in the first DPS, it is preferable that atleast 1 second of display time is ensured as a normal playback (orreproducing) time (e.g., PTS2>=PTS1+1 sec.). And, whenpalette_update_flag=1b in the second DPS, which indicates only themodification (or change) in the palette information, it is preferablethat at least 2 video frames of display time are ensured (e.g.,PTS4>=PTS 3+Duration of 2 video frames). In addition, although FIG. 7Billustrates an example of a fade out effect, a fade in effect may alsobe applied herein using the same principle.

The syntax structure of the above-described dialog style segment (DSS)and the dialog presentation segment (DPS) will now be described indetail with reference to FIGS. 8 to 10B. More specifically, byillustrating the structure of the syntax in detail, the usage of theabove-described style information and palette information according tothe present invention can be described with more precision. FIG. 8illustrates a syntax of the text subtitle stream (Text_subtitle_stream()) according to the present invention. Referring to FIG. 8, theText_subtitle_stream( ) includes a dialog_style_segment( ) syntax and adialog_presentation_segment( ) syntax. More specifically, thedialog_style_segment( ) syntax corresponds to a single dialog stylesegment (DSS) defining the style information set, and thedialog_presentation_segment( ) syntax corresponds to a plurality ofdialog presentation segments (DPS) having the actual dialog informationrecorded therein.

FIGS. 9A to 9D illustrate a detailed structure of thedialog_style_segment( ), which represent the dialog style segment (DSS).More specifically, FIG. 9A illustrates the overall structure of thedialog_style_segment( ), wherein a dialog_style set( ) defining diversestyle information sets that are applied in the dialog is defined. FIG.9B illustrates a dialog_style set( ) according to the present invention,which is defined in the dialog_style_segment( ). Apart from theregion_styles (region_style( )), the dialog_style_set( ) includes aPlayer_style_flag, a user_changeable_style set( ), and a palette( ). ThePlayer_style_flag indicates whether change in style information by theplayer is authorized. Also, the user_changeable_style set( ) defines therange of change in style information by the player, and the palette( )indicates color information.

The region style information (region_style( )) represents Global styleinformation defined for each region, as described above. Aregion_style_id is assigned to each region, and a style information setcorresponding to the specific region_style_id is defined. Therefore,when reproducing a dialog by recording the region_style_id, which isapplied to the corresponding dialog, within the dialog presentationsegment (DPS), style information set values defined by identicalregion_style_id within the dialog_style set( ) are applied, so as toreproduce the dialog. Accordingly, individual style information includedin the style information set provided to each region_style_id will nowbe described.

Herein, region_horizontal_position, region_vertical_position,region_width, and region_height are provided as information for definingthe position and size of a corresponding region within the screen. And,region_bg_color_entry_id information deciding a background color of thecorresponding region is also provided. More specifically, theregion_bg_color_entry_id information is a set of information designatinga specific palette_entry_id within the palette information, which willbe described in a later process with reference to FIG. 9D. Herein, theregion_bg_color_entry_id information uses the color information (Y, Crand Cb values) and degree of transparency (T value), which are assignedto the corresponding palette_entry_id, for background color of thecorresponding region.

In addition, as information defining an original (or starting) positionof the text within the corresponding region, a text_horizontal_positionand a text_vertical_position are provided. Also, a text_flow definingthe direction of the text (e.g., left→right, right→left, up→down), and atext_alignment defining the alignment direction of the text (e.g., left,center, right) are provided. More specifically, when a plurality ofregions are included in a specific dialog, the text_flow of each regionincluded in the corresponding dialog is defined to have an identicaltext_flow value, so as to prevent users from viewing disturbed images.

Furthermore, a line_space designating space between each line within theregion is provided as individual style information included in the styleinformation set. And, a font_type, a font_size, and afont_color_entry_id are provided as font information for actual fontinformation. More specifically, the font_color_entry_id is a set ofinformation designating a specific palette_entry_id within the paletteinformation, which will be described in a later process with referenceto FIG. 9D. Herein, the font_color_entry_id information uses the colorinformation (Y, Cr and Cb values), which is assigned to thecorresponding palette_entry_id, as a color value of the correspondingfont.

Meanwhile, the Player_style_flag recorded within the dialog_style set( )indicates whether an author may apply the style information provided tothe player. For example, when Player_style_flag=1b, as well as the styleinformation defined in the dialog_style set( ) recorded in a disc, theplayer is authorized to reproduce the text subtitle stream by applyingthe style information provided within the player itself. On the otherhand, when Player_style_flag=0b, only usage of the style informationdefined in the dialog_style set( ) recorded within the disc isauthorized.

FIG. 9C illustrates the user_changeable_style set( ) according to thepresent invention, which is defined in dialog_style set( ). Theuser_changeable_style set( ) pre-defines the types of style informationthat can be changed by the user and the range of change, and theuser_changeable_style set( ) is used for easily changing the styleinformation of the text subtitle data. However, when the user is enabledto change all style information, which are described in FIG. 9B, theuser may more confused. Therefore, in the present invention, the styleinformation of only the font_size, the region_horizontal_position, andthe region_vertical_position may be changed. And, accordingly, variationin the text position and the line space, which may be changed inaccordance with the font_size, is also defined in theuser_changeable_style set( ). More specifically, theuser_changeable_style set( ) is defined for each region_style_id. Forexample, a maximum of 25 user_style_id within a specificregion_style_id=k may be defined in the user_changeable_style set( ).

Also, each user_style_id includes region_horizontal_position_directionand region_vertical_position_direction information, which designate thedirection of the changed position of each of the changeableregion_horizontal_position and region_vertical_position. Eachuser_style_id also includes region_horizontal_position_delta andregion_vertical_position_delta information for designating a singleposition movement unit in each direction as a pixel unit. Morespecifically, for example, when region_horizontal_position_direction=0,the position of the region is moved to a right direction. And, whenregion_horizontal_position_direction=1, the position of the region ismoved to a left direction. Also, whenregion_vertical_position_direction=0, the position of the region ismoved to a downward direction. Finally, whenregion_vertical_position_direction=1, the position of the region ismoved to an upward direction.

Furthermore, each user_style_id includes font_size_inc_dec information,which designates the changing direction each of the changeablefont_size, and font_size_delta information for designating a singleposition movement unit in each direction as a pixel unit. Morespecifically, for example, font_size_inc_dec=0 represents an increasingdirection of the font_size, and font_size_inc_dec=1 represents adecreasing direction of the font_size. Moreover, the decrease orincrease of the “text position” and the “line space”, which are changeddepending upon the decrease or increase of the font_size, may be definedby the same method as that of the font_size, theregion_horizontal_position, and the region_vertical_position.

Accordingly, the characteristics of the user_changeable_style set( )according to the present invention will now be described as follows. Anidentical number of user_control_style( ) is defined in allregion_style( ) that are included in the dialog style segment (DSS).Accordingly, the number of user_control_style that can be applied to allof the dialog presentation segments (DPS) is also identical. Further,each user_control_style( ) is represented by a different user_style_id,and when the user selects a random user_id_style, an identical order ofthe user_control_style( ) is applied to all region_style( ). Inaddition, a combination of all changeable styles is defined in a singleuser_control_style( ). More specifically, the region_position, and thefont_size are defined simultaneously, instead of being definedseparately. Finally, each of the direction (*_direction) and theindication of increase or decrease (*_inc_dec) is recorded independentlyregardless of each position movement unit (*_delta). More specifically,by defining only the position movement unit (*_delta), a final value ofthe actually changed style information (or style value) may be obtainedby adding the position movement unit (*_delta) to the value defined inthe region_style( ).

FIG. 9D illustrates palette information (palette( )) according to thepresent invention, which is defined in the dialog_style set( ). Thepalette( ) provides color changing information of the text subtitle datarecorded within the dialog. Herein, the palette( ) includes a pluralityof palette_entries, wherein each palette_entry is described by apalette_entry_id. And, each palette_entry is provided with a specificbrightness value (Y_value), a specific color value (Cr_value, Cb_value),and a specific T_value, which designates the transparency of the textdata.

Accordingly, the brightness value (Y_value) is within the range of 16 to235, the color value (Cr_value, Cb_value) is within the range of 16 to240, and the T_value for designating the transparency is within therange of 0 to 255. More specifically, T_value=0 represents fulltransparency, and T_value=255 represents full opacity. In addition,T_value=0 is generally designated as a default value, so that T_value=0may represent full transparency. Therefore, the disc manufacturer (orAuthor) records the palette information for each palette_entry_id withinthe dialog style segment (DSS), wherein the palette information is usedin the entire text subtitle stream. Thus, a specific palette_entry_idmay be designated and used from the above-described style information.

FIGS. 10A and 10B illustrate a detailed structure of thedialog_presentation_segment( ), which represent the dialog presentationsegment (DPS) according to the present invention. FIG. 10A illustratesthe overall structure of the dialog_presentation_segment( ), wherein adialog_start_PTS and a dialog_end_PTS are defined. The dialog_start_PTSand the dialog_end_PTS designate the presentation time of thecorresponding dialog. Then, the dialog_presentation_segment( ) includesa palette_update_flag, which indicates a change of information withinthe corresponding dialog. As described above, whenpalette_update_flag=1b, a new palette information (palette( )) that isused only in the corresponding DPS is separately defined, instead of thecommonly used palette information, shown in FIG. 9D, within the DDS.Accordingly, the author uses the palette_update_flag, so as to allow awide range of applications. Most particularly, in order to produce (orrepresent) fade in/out effects, DPSs having only the palette informationmodified are consecutively provided (e.g., DPS #3 to DPS #5 shown inFIG. 7B), thereby visually providing a fade in or fade out effect of thetext subtitle to the user.

Subsequently, a dialog_region( ) that defines the region information isrecorded in the dialog_presentation_segment( ). In the presentinvention, a maximum of two regions is provided within a single dialog,and therefore, dialog_region( ) information is provided to each region.The dialog_region( ) includes region_style_id information andcontinuous_present_flag information. The region_style_id informationdesignates any one of the region styles, as shown in FIG. 9B, and thecontinuous_present_flag information identifies whether to perform aseamless reproduction with the previous dialog region. Further, textdata and region_subtitle( ) information are also included in thedialog_region( ). The text data is included in the actual correspondingregion, and the region_subtitle( ) information defines the local styleinformation.

FIG. 10B illustrates a region_subtitle( ) information defined within thedialog_region( ). Herein, the region_subtitle( ) is formed of a group(or pair) of a text string and an inline style information that isapplied to the text string. More specifically, in thedialog_presentation_segment( ), when palette_update_flag=1b, theregion_style_id and the region_subtitle( ) should be identical to thoseof a previous dialog style segment (DSS). In this case, thecontinuous_present_flag should be determined ascontinuous_present_flag=1b. More specifically, type=0x01 within theregion_subtitle( ) represents the text string. Therefore, a charactercode (char_data_byte) is recorded within the text_string( ).

In addition, when the type within the region_subtitle( ) is not equal totype=0x01, the region_subtitle( ) represents the inline styleinformation. For example, type=0x02 represents a change in the Font set,and so a font ID value designated by the corresponding ClipInfo isrecorded in a specific field (i.e., the inline_style_value( )), andtype=0x03 represents a change in the Font style, and so a correspondingfont style value is recorded in a specific field (i.e., theinline_style_value( )). Also, type=0x04 represents a change in the Fontsize, and a corresponding font size value is recorded in a specificfield (i.e., the inline_style_value( )), and type=0x05 represents achange in the Font color, and therefore, an index value designated bythe corresponding palette is recorded in a specific field (i.e., theinline_style_value( )). Furthermore, type=0x0A represents a line break.

More specifically, as described above, type=0x05 represents a change inthe Font color. In this case, a modified palette_entry_id is recorded inthe inline_style_value( ), thereby enabling the font color that isapplied to each text string to be modified. For example, the textportion “mountain” included in Region 1, as shown in FIG. 5C, is writtenas a text_string (e.g., text_string=“mountain”), yet the text portion isset to “inline_style type=0x05 (change in Font color)” as the localstyle information. And, by setting the text portion to“inline_style_value( )=palette_entry_id(k), the font color of thecorresponding text_string=“mountain” can be reproduced to have the colorinformation (Y, Cr and Cb values) and degree of transparency (T value)defined in the palette_entry_id(k), shown in FIG. 9D.

Hereinafter, the method and apparatus for reproducing the text subtitlestream recorded on the optical disc, as described above, will now bedescribed in detail with reference to FIGS. 11A and 11B. FIG. 11Aillustrates the apparatus for reproducing the optical disc focusing onthe decoder according to the present invention and, more particularly,illustrates an example of a text subtitle decoding part 40, which isseparately included. More specifically, the apparatus includes a packetidentifier (PID) filter 5 for separating input streams into videostreams, audio streams, graphic streams, and text subtitle streams basedon their packet identifiers, a video decoding part 20 for reproducingthe video streams, an audio decoding part 10 for reproducing the audiostreams, a graphic decoding part 30 for reproducing the graphic streams,and a text subtitle decoding part 40 for reproducing the text subtitlestreams.

The text subtitle streams may be extracted from an optical disc, or theycould be inputted from an additional external source, as shown in FIG.11A. For this reason, the apparatus includes a switch 6 which selects aninput data source. Therefore, if the text subtitle streams in MPEGformat are extracted from the optical disc, the switch 6 selects dataline A connected to the PID filter 5. On the other hand, if they areinputted through an additional external source, the switch 6 selectsdata line B which is connected to the external source.

The video decoding part 20, audio decoding part 10, graphic decodingpart 30 include a transport buffer 21, 11, and 31, respectively, forstoring a predetermined size of data streams to be decoded. A videoplane 23 and a graphic plane 33 are included in the video decoding part20 and graphic decoding part 30, respectively, for converting decodedsignals into displayable images. The graphic decoding part 30 includes acolor look-up table (CLUT) 34 for controlling color and transparencylevels of the displayable images.

When the text subtitle decoding part 40 receives one or more textsubtitle streams from the switch 6, all of these streams are initiallypreloaded into a subtitle preloading buffer (SPB) 41 at once. Assuming atypical size of a text subtitle stream file for a single language isabout 0.5 megabytes, the size of the subtitle preloading buffer 41should be determined based on the total number of the text subtitlestream files. For example, in order to ensure seamless presentation of atext subtitle when a user switches among subtitle stream filessupporting two languages, the size of the subtitle preloading buffer 41should be greater than or equal to 1 megabytes. The size of the subtitlepreloading buffer 41 should be large enough to preload all the requiredtext subtitle stream files at once.

The text subtitle streams are all preloaded in the buffer 41 and used,because the entire text subtitle stream can be recorded within a smallcapacity, as described above. Therefore, the text subtitle stream isrecorded as a separate file, thereby facilitating the reading and usageof the text subtitle data only. Moreover, since the entire text subtitledata is preloaded to the buffer, the buffer can be controlled moreeasily. In a specific type of optical recording and reproducingapparatus, provided that a buffer underflow does not occur, the textsubtitle stream may be reproduced in combination with the main AV data,in real-time, without preloading the text subtitle stream. Hereinafter,an example of the text subtitle stream being preloaded according to thepresent invention will now be given and described in detail.

The text subtitle decoding part 40 further includes a text subtitledecoder 42 which decodes one or more text subtitle streams stored in thesubtitle preloading buffer 41, a graphics plane 43 converting thedecoded subtitle stream(s) into displayable images, and a color look-uptable (CLUT) 44 controlling the color information (Y, Cr and Cb values)and transparency information (T value) of the converted images.

An image superimposition part 50 included in the apparatus shown in FIG.11A combines the images outputted from the video decoding part 20, thegraphic decoding part 30, and the text subtitle decoding part 40. Thesecombined images are displayed on a display screen. The video imagesoutputted from the video plane 23 of the video decoding part 20 aredisplayed as a background of the display screen, and the imagesoutputted from the graphic decoding part 30 and/or the text subtitledecoding part 40 are superimposed over the displayed video images. Forexample, if the output images of the graphic decoding part 30 areinteractive graphic images, the text subtitle images outputted from thetext subtitle decoding part 40 are initially superimposed over the videoimages by a first adder 52. Thereafter, the interactive graphic imagesare further superimposed over the subtitle-superimposed images by asecond adder 53. The apparatus shown in FIG. 11A further includes asystem decoder 4 for decoding input transport streams (e.g., MPEGtransport streams), and a microprocessor 3 for controlling operations ofall the mentioned components of the apparatus.

Reference will now be made in detail to a method for reproducing textsubtitle streams according to the present invention. When an opticaldisc is preloaded by an optical disc player, an example of which isillustrated in FIG. 11A, information required for reproduction of datarecorded on the disc is initially extracted from the disc and stored ina memory (not shown). When a particular title that associates with aPlayList is selected by a user, at least one complete (entire) textsubtitle stream file designated in the PlayList file is initiallypreloaded into the subtitle preloading buffer 41 and font files relatedto the subtitle stream file is preloaded into the font preloading buffer410.

For example, when a title that associates with the PlayList shown inFIG. 4 is selected by a user, text subtitle files for text subtitle clipNo. 1 (Korean) and text subtitle clip No. 2 (English) are initiallypreloaded into the subtitle preloading buffer 41. Also, font filesrelated to the text subtitle files, which may be designated in clipinformation files of the text subtitle clips, are preloaded into thefont preloading buffer 410. Thereafter, playback of the PlayList isstarted. During the playback of the PlayList, AV streams of main AVclips No. 1 and 2 are decoded by the audio decoding part 10 and thevideo decoding part 20, respectively, and selected one of the preloadedtext subtitle streams is decoded by the text subtitle decoder 42. Thenthe decoded text subtitle images are superimposed over the decoded mainvideo images, and the entire images are displayed on a display screen.

As described above, when all operations are completed, and when the mainvideo data that is controlled by the PlayItem is displayed onto thescreen, the related text subtitle is superimposed through the imagesuperimposition part 50 (shown in FIG. 11A). And, as the superimposedtext subtitle is provided, the decoding of the text subtitle stream isinitiated. Meanwhile, in order to perform decoding of the text subtitlestream, a region style information and palette information within thedialog style segment (DSS), which configures the first packet stream(PES), are separately read and stored for later usage when reproducingthe DPS. Most particularly, when the palette information is read, thepalette information is simultaneously provided to the CLUT 44, so as toprovide the color and transparency desired by the user, when displayingthe text subtitle onto the screen.

FIG. 11B illustrates the text subtitle decoder 42, shown in FIG. 11A, inmore details. The decoding process performed by the text subtitledecoder 42 includes parsing, rendering, and composition steps. In theparsing step, the text subtitle stream(s) stored in the subtitlepreloading buffer (SPB) 41 is parsed into composition information,rendering information, and dialog text data, in accordance with theinformation included in the dialog presentation segment (DPS). A dialogrepresents all the text subtitles that are displayed during apredetermined period of time, which may be defined by a presentationtime stamp (PTS). Accordingly, the composition information correspondsto the information related to the display time and display position ofthe text subtitle when displayed onto the screen, and also to a newpalette information that is newly defined by a palette informationupdate (palette_update_flag=1b). The rendering information correspondsto the information that actually describe (or represent) the text ofeach region for each dialog. Such rendering information includes “regionwidth & height”, “Background color”, “Text Flow”, “Text Alignment”, and“Font id/style/size”. Furthermore, the dialog text informationcorresponds to an inline style information that is applied to the actualtext data and a specific text string recorded within the DPS.

Referring to FIG. 11B a text subtitle processor 421 included in the textsubtitle decoder 42 parses the subtitle stream file(s) stored in thesubtitle preloading buffer 41 into composition and rendering informationand dialog text data. The composition and rendering information is thenstored in a dialog composition buffer (DCB) 425, and the dialog textdata are stored in a dialog buffer (DB) 422. More specifically, apalette update information (palette_update_flag=1b) is included in thecomposition information, which is parsed by the parsing step. And, whenpalette_update_flag=0b, the common palette information, which wasinitially provided from the dialog style segment (DSS) to the CLUT 44,may be used continuously without being updated. Conversely, whenpalette_update_flag=1b, the common palette information within the DSS isignored, and a new palette information is newly defined within thecorresponding DPS and is updated to the CLUT 44 and used. However, whenthe presentation (or reproduction) of the corresponding DPS iscompleted, the palette update is cleared, and the common paletteinformation initially provided from the CLUT 44 is used once again. Atthis point, the update of the CLUT 44 should be completed before thepresentation (or reproduction) of the subsequent DPS.

In the rendering step, the parsed dialog text data are rendered intobitmap data using the rendering information, which represents styleinformation required for rendering the dialog text data. A text renderer423 renders the dialog text data stored in the dialog buffer 422 intobitmap data under control of a dialog presentation controller 426. Inorder to perform the rendering function, the text renderer 423 receivesfont data associated with the dialog text data from the font preloadingbuffer 410, receives rendering information and inline style informationfrom the dialog presentation controller 426, and renders the dialog textdata into bitmap data using the rendering information and inline styleinformation, which is applicable for each text string of the dialog textdata. Thereafter, the rendered text data are then stored in a bitmapobject buffer (BOB) 424 as a bitmap object. Accordingly, the “Object”being recorded in the BOB buffer 424 corresponds to the text data ofeach region within each dialog, which is converted to a bitmap object.Therefore, a maximum of 2 objects for each region is parsed and storedwithin the BOB buffer 424.

Finally, in the composition step, the rendered text data are added intothe graphics plane (GP) 43 according to the composition information,which represents information indicating time for displaying a textsubtitle within the display screen. Finally, the bitmap object stored inthe bitmap object buffer 424 is transferred (added) to the graphicsplane 43 according to the composition information provided by the dialogpresentation controller 426. The color look-up table 44 uses paletteinformation included in the composition information to adjust color andtransparency levels of an output of the graphics plane 43.

Accordingly, in the DPS of palette_update_flag=1b, the rendering step isomitted, and the bitmap object related to a previous DPS and which isstored within the BOB buffer 424 is preserved and used. Herein, by usingthe palette information defined in the DPS of palette_update_flag=1b, soas to modify the CLUT only, only the color information (Y, Cr, and Cbvalues) and transparency information (T value) for the bitmap object ofthe previous DPS, which is preserved in the graphics plane, are updated.As described above, this is referred to as “palette_only displayupdate”. By using the “palette_only display update”, the fade in/outeffects of the DPS may also be represented.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A method of reproducing text subtitle streams, the method comprising:receiving at least one text subtitle stream from an external source,each text subtitle stream, including a style segment defining a group ofregion styles and a plurality of presentation segments, eachpresentation segment containing at least one region of text and eachregion of text being linked to a selected one of the group of regionstyles, wherein the style segment further defines palette information,and each presentation segment further contains a palette update flagwhich indicates whether to use the palette information defined in thestyle segment or to use new palette information when reproducing theeach presentation segment; and decoding the text subtitle stream usingthe style segment defining the group of region styles and thepresentation segment including the palette update flag.
 2. The method ofclaim 1, wherein when the palette update flag indicates the use of thenew palette information, the new palette information is defined in theeach presentation segment.
 3. The method of claim 1, wherein the paletteupdate flag is set to “1b” to indicate the use of the new paletteinformation.
 4. A method of recording text subtitle streams, the methodcomprising: receiving at least one text subtitle stream from an externalsource, each text subtitle stream, including a style segment defining agroup of region styles and a plurality of presentation segments, eachpresentation segment containing at least one region of text and eachregion of text being linked to a selected one of the group of regionstyles, wherein the style segment further defines palette information,and each presentation segment further contains a palette update flagwhich indicates whether to use the palette information defined in thestyle segment or to use new palette information when reproducing theeach presentation segment; and recording the received text subtitlestream in a recording medium.
 5. A method of reproducing text subtitlestreams, the method comprising: receiving at least one text subtitlestream from an external source, each text subtitle stream, including astyle segment defining a group of region styles and a plurality ofpresentation segments, each presentation segment containing at least oneregion of text and each region of text being linked to a selected one ofthe group of region styles, wherein the presentation segment furthercontains a palette update flag which indicates display update only inpalette information in association with a immediately previouspresentation segment when reproducing each presentation segment; anddecoding the text subtitle stream using the style segment defining thegroup of region styles and the presentation segment including thepalette update flag.
 6. A method of reproducing text subtitle streams,the method comprising: receiving at least one text subtitle stream froman external source, each text subtitle stream including a style defininga group of region styles and palette information, a first presentationsegment configured to use the palette information defined in the stylesegment, and at least one second presentation segment configured tofade-in or fade-out a presentation of the first presentation segment bychanging its palette information only, each one of the first and secondpresentation segments containing at least one region of text and eachregion of text being linked to a selected one of the group of regionstyles defined in the style segment decoding the text subtitle streamusing the style segment defining the group of region styles and thepresentation segment including the palette update flag.
 7. The method ofclaim 6, wherein the changed palette information is defined in thesecond presentation segment.
 8. A method of reproducing text subtitlestreams, the method comprising: selecting at least one text subtitlestream from an external source or a recording medium, each text subtitlestream, including a style segment defining a group of region styles anda plurality of presentation segments, each presentation segmentcontaining at least one region of text and each region of text beinglinked to a selected one of the group of region styles, wherein thestyle segment further defines palette information, and each presentationsegment further contains a palette update flag which indicates whetherto use the palette information defined in the style segment or to usenew palette information when reproducing the each presentation segment;and decoding the text subtitle stream using the style segment definingthe group of region styles and the presentation segment including thepalette update flag.
 9. A method of reproducing text subtitle streams,the method comprising: selecting at least one text subtitle stream froman external source or a recording medium, each text subtitle stream,including a style segment defining a group of region styles and aplurality of presentation segments, each presentation segment containingat least one region of text and each region of text being linked to aselected one of the group of region styles, wherein the presentationsegment further contains a palette update flag which indicates displayupdate only in palette information in association with a immediatelyprevious presentation segment when reproducing each presentationsegment; and decoding the text subtitle stream using the style segmentdefining the group of region styles and the presentation segmentincluding the palette update flag.
 10. A method of reproducing textsubtitle streams, the method comprising: selecting at least one textsubtitle stream from an external source a recording medium, each textsubtitle stream, each text subtitle stream including a style defining agroup of region styles and palette information, a first presentationsegment configured to use the palette information defined in the stylesegment, and at least one second presentation segment configured tofade-in or fade-out a presentation of the first presentation segment bychanging its palette information only, each one of the first and secondpresentation segments containing at least one region of text and eachregion of text being linked to a selected one of the group of regionstyles defined in the style segment decoding the text subtitle streamusing the style segment defining the group of region styles and thepresentation segment including the palette update flag.
 11. An apparatusfor reproducing a text subtitle stream, the apparatus comprising:decoder configured to decode the text subtitle stream from the externalsource, the text subtitle stream including a style segment defining agroup of region styles and a plurality of presentation segments, eachpresentation segment containing at least one region of text and eachregion of text being linked to a selected one of the group of regionstyles, wherein the style segment further defines palette information,and each presentation segment further contains a palette update flagwhich indicates whether to use the palette information defined in thestyle segment or to use new palette information when reproducing theeach presentation segment; and controller configured to controloperation of the decoder to receive the text subtitle stream from areceiver and decode the text subtitle stream using the region stylesdefined in the style segment and the palette update flag defined in thepresentation segment.
 12. An apparatus for reproducing a text subtitlestream, the apparatus comprising: decoder configured to decode the textsubtitle stream from the external source, the text subtitle streamincluding a style segment defining a group of region styles and aplurality of presentation segments, each presentation segment containingat least one region of text and each region of text being linked to aselected one of the group of region styles, wherein the presentationsegment further contains a palette update flag which indicates displayupdate only in palette information in association with a immediatelyprevious presentation segment when reproducing each presentationsegment; and controller configured to control operation of the decoderto receive the text subtitle stream from a receiver and decode the textsubtitle stream using the region styles defined in the style segment andthe palette update flag defined in the presentation segment.
 13. Anapparatus for reproducing a text subtitle stream, the apparatuscomprising: decoder configured to decode the text subtitle stream fromthe external source, the text subtitle stream including a style defininga group of region styles and palette information, a first presentationsegment configured to use the palette information defined in the stylesegment, and at least one second presentation segment configured tofade-in or fade-out a presentation of the first presentation segment bychanging its palette information only, each one of the first and secondpresentation segments containing at least one region of text and eachregion of text being linked to a selected one of the group of regionstyles defined in the style segment; and controller configured tocontrol operation of the decoder to receive the text subtitle streamfrom a receiver and decode the text subtitle stream using the regionstyles defined in the style segment and the palette update flag definedin the presentation segment.